Secondary recovery operation



1960 w. o. HElLMAN ET AL 2,924,276

SECONDARY RECOVERY OPERATION Filed Aug. 8, 1955 mzEoE k =o 32$ 28 MEEQEInventors William O. Hellman James A. Reilly Byg. Q.

Attorney United States Patent @fitice SECONDARY RECOVERY OPERATIONWilliam 0. Hellman, Short Hills, and James A. Refill, Westfield, N.J.,amignors, by mesne assignments, to Jersey Production Research CompanyApplication August 8, 1955, Serial No. 526,942

3 Claims. (Cl. 16611) The present invention is broadly concerned with animproved method for increasing the recovery of crude petroleum oil fromoil-bearing subsurface formations. The invention is more particularlyconcerned with a particular integrated combination of steps wherein lowboiling liquid solvents are used in conjunction with a natural gas drivefollowed by the use of a combustion front which is caused to movethrough the subsurface strata from an input to an output well. Inaccordance with the present invention a quantity of a low boiling liquidsolvent which is substantially completely miscible with crude oil isinjected through an input well into an oil reservoir and maintained in aliquid bank or pool of relatively high concentration as it is impelledthrough the reservoir. This liquid bank of solvent which is driven by agas drive effectively washes out the crude oil in the reservoir. Thedriving pressure of the driving gas is utilized to advance the bank ofliquid solvent through the reservoir. Substantially complete recovery ofthe solvent is obtained by its vaporization into the driving gas. Thefinal phase of this integrated process is to initiate a combustion frontat the input Well and to cause this front to pass through the reservoirto the output well.

In accordance with the present invention the liquid propane or othermaterial is caused to flow through the field to another point or area inthe field propelled by a stream of natural gas. Air, oxygen, or otheroxygen-containing gas is then injected at the input well and acombustion front caused to move from the input to the output well.

In the first phase of the present operation after the band of propanehas moved sufficiently far through the formation, it becomes relativelyrich in recovered oil. It is within the scope of the present inventionto remove at least a portion or" the band of propane containing thedissolved oil at this point; to segregate the recovered oil from thepropane and to return the propane to the formation in order to assist inmaintaining the liquid bank of concentrated solvent.

Furthermore, the natural gas driven propane band strips and recovers theresidual propane from depleted portions of the formation and thusrecovers appreciable amounts of propane which otherwise would be lost inthe formation. Since the natural gas flows more rapidly through theformation than the propane or oil, some propane is carried forward andthrough the bank. However, this propane vaporized in the natural gas isabsorbed from the gas by the oil ahead of the propane band. By theseactions the maintenance of a concentrated band of propane is promoted.

It is also within the scope of the present invention to bring thereservoir up to the desired working pressure 2,924,276 Patented Pole.2*, 1960 Id input well. This combustion front passes through thereservoir, serves to heat up the reservoir and thereby secures a greaterrecovery of the injected propane and of the remaining oil.

The invention may be readily understood by reference to the drawingillustrating the same. Referring specifically to Fig. 1, anoil-producing formation 1-0 is shown disposed below the surface of theearth 1. Well bore holes 2, 3, 4, 5 and 6 are shown extending from thesurface of the earth through substrata to near the bottom of oil-bearingformation it In accordance with one concept of the present invention, apredetermined amount of liquefied propane or an equivalent material isintroduced by means of bore hole 6 into the oil-producing sand 10 and isthen followed by a continuous injection of a suitable natural gas intohere hole 6. The band of propane is shown disposed between well boreholes 4 and 5, flowing in the direction of bore holes 3 and 2. Oil iswithdrawn from core holes 3 and 3 together with gas which is separatedfrom the oil at the surface and recycled to injection well Since theband of propane has moved from bore hole 6 to bore hole 4, the front endof the band contains dissolved ther in substantial amounts of oil. Thus,in accordance with one concept of the present invention, a portion ofthis fluid may be withdrawn from the reservoir by means of bore hole 4.The oil is segregated from the propane by any suitable means such asdistillation and passed to suitable storage. The segregated propane ispreferably returned to the formation by means of well bore hole 5immediately back of the bank of propane in the formation and ahead ofthe natural gas drive.

The natural gas introduced by means of well 6 serves both to drive theoil and propane bank forward and to remove the residual propane from theoil-depleted zone of the formation by vaporization. At this point anoxygen-containing gas such as air or oxygen is introduced into well 6and ignited. The oxygen-containing gas is continued to be injected into6 and the flame front thus advances through the reservoir from well 6 towell 3 thereby increasing the recovery of propane and oil.

The present invention is broadly concerned with a novel procedure forthe recovery of oil from reservoirs. In accordance with the presentprocess, a band of relatively volatile liquid miscible with oil, as forexample, C and C hydrocarbons is caused to flow through the formation.This band of liquid is caused to flow by utilizing a natural gas drive.The gas drive tends to recover from the formation the solvent used toWash out the oil. By operating as described, eiiicient recovery of theoil is secured through the use of a limited amount of propane or anequivalent solvent. Furthermore, efficient recovery of residual propanefrom the formation is readily secured.

A specific concept of the present invention is to employ the operationin conjunction with a plurality of spaced bore holes in a particularreservoir. A solvent such as liquefied propane is introduced by means ofone bore hole in a sufficient quantity followed by the introduction ofnatural gas through the same bore hole. The band or bank of propane iscaused to How through the formation past a second spaced bore hole inthe direction of a third spaced bore hole. That portion of the propanebank which has flowed from the first to the third bore hole containsappreciable quantities of recovered oil and can be withdrawn to thesurface. The oil is separated from the propane which is preferablyreturned to the formation by means of the second bore hole, thusinterposing the recovered and concentrated propane at a point near therear of the propane bank and ahead of the gas injection point. Therearrnost portion of the propane bank being relatively free of oilconstituents has a very high solvency power and readily strips the oilformation of remaining oil constituents. Thus, the bank of propane as itflows through the formation by the operation described has a relativelyhigh quantity of oil in the front end of the pool and is relatively freeof oil at the rear end of the moving pool, thus serving to moreefficiently remove oil from the formation.

The recovery method of the present invention involves the utilization ofa bank of liquid propane or other light hydrocarbons or otheroil-miscible material such as CO by passing these liquid substancesthrough producing formations. The solvent can either be introduced as agas or liquid but the conditions should be such as will result in theformation of a liquid solvent in the reservoir in the form of a bank orband. The bank is driven forward by introduction of natural gas, fluegas, inert gas, air, or combinations of these back of the bank ofsolvents. The producing formation is subject to a washing action by thebank of propane or other material and, as a consequence, there is littleoil left in the formation that has been washed. Some oil may be left dueto irregularity in flow due to the fact that producing formations arenot homogeneous. The gas flowing back of the bank would have residualliquid, propane, or other material vaporized into it because of the lowpartial pressure of these materials in the gas. Thus, the liquid propaneor other materials being recovered from the formation through thisevaporation procedure pass along through the formation with the gas. Inaccordance with the present invention, the oil is in part recovered fromthe formation by being increased in volume and reduced in viscosity bydilution with the solvent; but a major contribution to completeness ofrecovery results from the washing of the sand with the solvent. 7

As the propane travels forward, it drives ahead of it liquid oil whichcan be recovered as such, with little or no propane in it up to acertain point. Back of a liquid oil layer is a layer of a mixture ofpropane and oil which is preferably also produced, that is, drawn from awell; the propane may then be recovered and cycled back to the formationat a proper point. The gas used to drive the bank of solvent movesfaster than the solvent itself, and as a result, it tends to carrypropane as vapor from the propane layer into the oil layer where thepropane is absorbed. This absorption action tends to prevent excessivewidening of the zone of oil-propane mixture.

With respect to specific operating conditions, as for example pressure,they of necessity depend upon various field conditions such as depth ofoil-producing formation and temperature of the reservoir. Among otherfactors controlling operating conditions is the solvent employed. Ingeneral, the practicable, useful control measure is the pressure of theoperation required in order to promote the maintenance of a relativelyconcentrated band of the solvent material. In general, the pressureshould be such as to maintain relatively pure solvent in the liquidcondition, which pressure is at least equivalent to or more generally inexcess of the vapor pressure of the solvent at the reservoirtemperature.

Generally speaking, reservoir temperatures are in the range of from 100F. to 250 F., although lower reservoir temperatures and higher have attimes been incurred. Usual reservoir temperatures are in the range fromabout 150 F. to 200 F. Under typical reservoir conditions, the vaporpressure of propane will be from about 200 to 600 pounds per squareinch, and if propane is employed, pressures of this order or higher mayconveniently be employed.

With respect to the rate of recycling of the gas, this quantity will ingeneral be set at the economic optimum which reflects the pressurelevel, permeability of the formation, separation of the injection andproducing wells, etc.

As indicated above, the present invention broadly relates to acombination of solvent extraction and combustion steps for obtaining oilfrom a subterranean reservoir. In accordance with one embodiment of theinvention, a bank of an oil solvent such as liquefied propane isinjected into a reservoir to be followed by natural gas substantially inthe form of a second bank. In both of these instances it will beunderstood that the term bank implies an effective volume of liquefiedpropane or natural gas which is less than the pore volume of thereservoir. In the case of the liquefied propane or other solvent, thevolume of propane should constitute between 0.1 and 0.5 and preferably0.25 and 0.4 hydrocarbon volume of the reservoir. In the case of thenatural gas, the minimum amount of this component is fixed by the factthat the combustion front following the bank of natural gas should nevercontact or extend to the bank of propane. In other words, the bank ofnatural gas should be less in volume than the pore volume of thereservoir but always sufiicient in volume to prevent actual contactbetween the following combustion front and the bank of propane.

Once the bank of natural gas has been injected into the reservoir behindthe bank of liquefied propane, a combustion front is initiated byinjecting and igniting a combustible mixture of gases immediately behindthe bank of natural gas. It will be understood that a great number ofcombustible gas mixtures may be employed, but a mixture of natural gasand air is preferred for this purpose. The injection of the combustiblegas mixture and its subsequent combustion is continued untilsubstantially all of the oil and propane within the reservoir isrecovered. With this procedure virtually complete recovery of theseconstituents is contemplated.

The entire mechanism of the procedure just described is not entirelyunderstood at this time, but it appears that the propane or othersolvent dissolves and displaces the oil from within a reservoir. Thefollowing bank of natural gas acts to vaporize and remove residualamounts of propane and/or oil that are left within the reservoir behindthe bank of propane and/or oil which is left behind in the reservoirfollowing the preceding steps of the process. The combustion front,however, never contacts the bank of propane itself with the result thatnone of the propane is consumed by the process. Thus, attractiverecoveries of both oil and solvent are made possible.

Another method of employing the integrated process of the presentinvention is to inject natural gas at the input well until substantiallyall the propane is recovered from the formation and the gases from theoutput Well contain a low concentration of propane. At this point thereservoir between the input and output well contains residual oil, asmall quantity of propane and natural gas. An oxygen-containing gas suchas air or oxygen is introduced into the formation at the input well.Injection of the oxygen-containing gas is continued until the gases fromthe output well contain oxygen in suificient concentration to supportcombustion. A flame or combustion front is then initiated at the inputwell which will propagate itself to the output well, since the reservoircontains a blend of natural gas and combustion supporting gas. In someinstances the injection of the oxygencontaining gas at the input wellwill tend to deplete the formation of natural gas about the input welland thus combustion will not be supported. Under these conditions thegas removed from the output well which contains sufficient oxygen tosupport combustion is recycled to the formation in the area about theinput well by means of the input well. Combustion is then initiated. Bythis technique in many instances it is possible to initiate a detonationor explosive wave from the input well to the output well which willserve to fracture the formation and produce additional fissures throughwhich additional oil may flow and be recovered. A very desirable methodof operation is to block off or seal the input well prior to ignitingthe combustion front whereby a blowback in the input well is avoided anda greater pressure drive in the direction of the output well is secured.

Having described the invention it is claimed:

1. Improved process for the recovery of hydrocarbon from an oil bearingsubstrata which comprises introducing a liquid pool of a normallygaseous hydrocarbon into said substrata by means of an input well,impelling said liquid pool through said formation to an output well bymeans of a natural gas drive introduced by means of said input well,continuing the introduction of said natural gas into said input welluntil the gases removed from said output well have a relatively lowconcentration of said normally gaseous hydrocarbon, then introducing anoxygen-containing gas into said substrata until said gases from saidoutput well have a concentration of oxygen sufficient to supportcombustion, thereafter initiating a combustion front at said input well,whereby said combustion front will progress to said output well, saidgases removed from said output well which have a relatively lowconcentration of normally gaseous hydrocarbons and which have aconcentration of oxygen sufficient to support combustion being recycledto said input well prior to initiating said combustion front.

2. Process as defined by claim 1 wherein said normally gaseoushydrocarbon comprises propane.

3. Process as defined by claim 2 wherein said input well is blocked offprior to initiating said combustion front, whereby a pressure drive isexerted in the direction 10 of said output well.

References Cited in the file of this patent UNITED STATES PATENTS1,457,479 Wolcott June 5, 1923 15 2,642,943 Smith June 23, 1953 FOREIGNPATENTS 696,524 Great Britain Sept. 2, 1953 726,712 Great Britain Mar.23, 1955

1. IMPROVED PROCESS FOR THE RECOVERY OF HYDROCARBON FROM AN OIL BEARINGSUBSTRATA WHICH COMPRISES INTRODUCING A LIQUID POOL OF A NORMALLYGASEOUS HYDROCARBON INTO SAID SUBSTRATA BY MEANS OF AN INPUT WELL,IMPELLING SAID LIQUID POOL THROUGH SAID FORMATION TO AN OUTPUT WELL BYMEANS OF A NATURAL GAS DRIVE INTRODUCED BY MEANS OF SAID INPUT WELL,CONTINUING THE INTRODUCTION OF SAILD NATURAL GAS INTO SAID INPUT WELLUNTIL THE GASES REMOVED FROM SAILD OUTPUT WELL HAVE A RELATIVELY LOWCONCENTRATION OF SAID NORMALLY GASEOUS HYDROCARBON, THEN INTRODUCING ANOXYGEN-CONTAINING GAS INTO SAID SUBSTRATA UNTIL SAID GASES FROM SAIDOUTPUT WELL HAVE A CONCENTRATION OF OXYGEN SUFFICIENT TO SUPPORTCOMBUSTION, THEREAFTER INITIATING A COMBUSTION FRONT AT SAID INPUT WELL,WHEREBY SAID COMBUSTION FRONT WILL PROGRESS TO SAID OUTPUT WELL, SAIDGASES REMOVED FROM SAID OUTPUT WELL WHICH HAVE A RELATIVELY LOW CON-